A water-based scratch-off masking black ink, its preparation method and application

Abstract

This invention provides a water-based scratch-off opaque black ink, its preparation method, and its application, belonging to the field of printing technology. The water-based scratch-off opaque black ink provided by this invention, by weight, comprises the following components: 30-45 parts of core-shell structured acrylic emulsion, 15-25 parts of aliphatic waterborne polyurethane dispersion, 12-20 parts of carbon black, 4-8 parts of modified polyethylene wax powder, 2-4 parts of superdispersant, 0.5-1.5 parts of wetting and leveling agent, 0.2-0.8 parts of defoamer, 0.1-0.5 parts of pH adjuster, 15-25 parts of water, and 1-3 parts of additives. The results of the embodiments show that the ink layer formed by the water-based scratch-off opaque black ink provided by this invention exhibits excellent scratchability at room temperature, high temperature, and low temperature, and the scratched area has neat edges without burrs or residue; the ink layer does not crack when bent at low temperatures of -5 to 5°C, exhibiting excellent bending resistance, and peels off in continuous flakes without generating dust.

Description

Technical Field

[0001] This invention relates to the field of printing technology, and in particular to a water-based scratch-off opaque black ink, its preparation method, and its application. Background Technology

[0002] Water-based scratch-off cover ink is widely used in industries such as lottery, tickets, invoices, telecommunications, IT, commerce, and education. Examples include telephone recharge cards, game cards, internet access cards, lottery cards, learning cards, anti-counterfeiting identification cards, scratch-off booklets, and children's scratch art. While existing water-based scratch-off cover inks offer excellent coverage, their strong adhesion causes products to easily stick together during transportation, making separation difficult and even damaging them, leading to spoilage. Furthermore, water-based scratch-off cover inks have poor freeze resistance; the ink layer easily crumbles when scratched at low temperatures, generating significant dust pollution. They are also prone to cracking when bent at low temperatures, severely hindering their promotion and application.

[0003] Therefore, how to improve the adhesion of the ink layer, enhance its low-temperature bending resistance, and prevent it from crumbling when scraped at low temperatures has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a water-based squeegeeable cover ink, its preparation method, and its application. The water-based squeegeeable cover ink provided by this invention will not stick together when the ink layers are stacked, and it has excellent bending resistance at low temperatures. When squeegeed at low temperatures, it falls off in continuous flakes without generating dust.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a water-based, scratch-off, opaque black ink, comprising the following components by weight: 30-45 parts of core-shell structured acrylic emulsion, 15-25 parts of aliphatic waterborne polyurethane dispersion, 12-20 parts of carbon black, 4-8 parts of modified polyethylene wax powder, 2-4 parts of superdispersant, 0.5-1.5 parts of wetting and leveling agent, 0.2-0.8 parts of defoamer, 0.1-0.5 parts of pH adjuster, 15-25 parts of water, and 1-3 parts of additives; The core-shell structured acrylic emulsion comprises a shell polymerized from acrylate monomers and olefinically unsaturated acid monomers, and a core polymerized from acrylate monomers and styrene.

[0006] Preferably, the core-shell structured acrylic emulsion is prepared from raw materials comprising the following components by mass: 100 parts of acrylate monomers, 0.1-10 parts of olefinic unsaturated acid monomers, 1-20 parts of styrene, 0.05-2 parts of emulsifier, 0.05-1 part of initiator, 0.1-3 parts of neutralizer, 0.001-0.005 parts of catalyst, 0.1-0.5 parts of oxidant, 0.1-1 parts of reducing agent, and 60-150 parts of water.

[0007] Preferably, the acrylate monomers are alkyl acrylates and / or alkyl methacrylates; the alkyl acrylates include one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, isooctyl acrylate, n-propyl acrylate, and cyclohexyl acrylate; the alkyl methacrylates include one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-propyl methacrylate, cyclohexyl methacrylate, tridecyl methacrylate, and octadecyl methacrylate.

[0008] Preferably, the olefinic unsaturated acid monomer is acrylic acid and / or methacrylic acid.

[0009] Preferably, the catalyst is ferrous sulfate heptahydrate and ethylenediaminetetraacetic acid disodium dihydrate; the mass ratio of ferrous sulfate heptahydrate to ethylenediaminetetraacetic acid disodium dihydrate is (1~2):(1~2).

[0010] Preferably, the preparation method of the core-shell structured acrylic emulsion includes the following steps: 1) Mix some acrylate monomers, olefinic unsaturated acid monomers, emulsifiers, initiators and some water to carry out the first polymerization reaction, and then add a neutralizing agent to obtain a shell emulsion; 2) Add the remaining acrylate monomers, styrene, catalyst, oxidant, reducing agent and remaining water to the shell emulsion obtained in step 1) to carry out a second polymerization reaction, and then filter to obtain a core-shell structured acrylic emulsion.

[0011] Preferably, the additive is a mixture of polyethylene glycol, tributoxyethyl phosphate and nano silica.

[0012] Preferably, the mass ratio of polyethylene glycol, tributoxyethyl phosphate and nano silica is 5:(2~3):(2~3).

[0013] This invention provides a method for preparing the water-based scratch-off opaque black ink described in the above technical solution, comprising the following steps: (1) Mix water, superdispersant, part of defoamer and carbon black to obtain carbon black slurry; (2) Mix the carbon black paste, core-shell structured acrylic emulsion and aliphatic waterborne polyurethane dispersion obtained in step (1), then add wetting and leveling agent, additives, remaining defoamer, modified polyethylene wax powder and pH adjuster, and finally filter to obtain waterborne scrapable cover black ink.

[0014] This invention provides the application of the water-based scratch-off opaque black ink described in the above technical solution or the water-based scratch-off opaque black ink prepared by the preparation method described in the above technical solution in the flexographic printing preparation of instant lottery tickets, prize-winning invoices or anti-counterfeiting labels.

[0015] This invention provides a water-based, scratch-off, opaque black ink, comprising the following components by weight: 30-45 parts of core-shell structured acrylic emulsion, 15-25 parts of aliphatic waterborne polyurethane dispersion, 12-20 parts of carbon black, 4-8 parts of modified polyethylene wax powder, 2-4 parts of superdispersant, 0.5-1.5 parts of wetting and leveling agent, 0.2-0.8 parts of defoamer, 0.1-0.5 parts of pH adjuster, 15-25 parts of water, and 1-3 parts of additives; wherein the core-shell structured acrylic emulsion comprises a shell layer polymerized from acrylate monomers and olefinic unsaturated acid monomers, and a core layer polymerized from acrylate monomers and styrene. In this invention, the core of the core-shell structured acrylic emulsion provides the coating with sufficient brittleness, allowing it to be cut off by a blade and peel off in sheets during scraping, rather than being stretched into filaments or torn incompletely. The outer shell provides flexibility and cohesion, preventing the coating from cracking due to excessive brittleness during drying or storage, while ensuring that it is scraped off in sheets rather than as powder. This "soft on the outside and hard on the inside" core-shell design ensures that the coating has sufficient strength to maintain complete coverage at room temperature, and breaks cleanly along the stress point when subjected to shear force, achieving an easy-to-scrape, dust-free, and clear-edged user experience. The film formed by the aliphatic waterborne polyurethane dispersion has high tensile strength and hardness. This characteristic allows the ink layer formed by the waterborne scrapeable opaque black ink to be relatively "brittle," satisfying the physical basis for scrapeability. The modified polyethylene wax powder provides the ink layer with excellent scratch resistance and anti-sticking properties, while giving the surface a smooth but not greasy feel, protecting the ink layer without causing slippage during scraping due to excessive smoothness. The results of the embodiments show that the ink layer formed by the water-based squeezable cover black ink provided by the present invention has excellent squeezability at room temperature, high temperature and low temperature, excellent high temperature resistance and freeze resistance, and the edge of the squeezed area is neat, without burrs or residue; the ink layer does not crack when bent at a low temperature of -5~5℃, has excellent bending resistance, and falls off in continuous flakes when squeezed, without generating dust; the water-based squeezable cover black ink will not stick together even when stacked after printing, and can be easily separated. Detailed Implementation

[0016] This invention provides a water-based, scratch-off, opaque black ink, comprising the following components by weight: 30-45 parts of core-shell structured acrylic emulsion, 15-25 parts of aliphatic waterborne polyurethane dispersion, 12-20 parts of carbon black, 4-8 parts of modified polyethylene wax powder, 2-4 parts of superdispersant, 0.5-1.5 parts of wetting and leveling agent, 0.2-0.8 parts of defoamer, 0.1-0.5 parts of pH adjuster, 15-25 parts of water, and 1-3 parts of additives; The core-shell structured acrylic emulsion comprises a shell polymerized from acrylate monomers and olefinically unsaturated acid monomers, and a core polymerized from acrylate monomers and styrene.

[0017] By weight, the water-based scratch-off masking black ink provided by this invention comprises 30-45 parts of a core-shell structured acrylic emulsion; the core-shell structured acrylic emulsion comprises a shell layer polymerized from acrylate monomers and olefinically unsaturated acid monomers, and a core layer polymerized from acrylate monomers and styrene. As one embodiment, the weight percentage of the core-shell structured acrylic emulsion can be 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, or 44 parts.

[0018] In this invention, the core-shell structured acrylic emulsion is prepared from raw materials comprising the following components by mass: 100 parts of acrylate monomers, 0.1-10 parts of olefinic unsaturated acid monomers, 1-20 parts of styrene, 0.05-2 parts of emulsifier, 0.05-1 part of initiator, 0.1-3 parts of neutralizer, 0.001-0.005 parts of catalyst, 0.1-0.5 parts of oxidant, 0.1-1 parts of reducing agent, and 60-150 parts of water.

[0019] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 100 parts by weight of acrylate monomers. In the present invention, during the preparation of the shell structure of the acrylic emulsion, the acrylate monomers diffuse into the micelles formed by the self-assembly of emulsifier molecules through aqueous diffusion. Free radicals initiate chain growth reactions in the monomers, resulting in free radical copolymerization. The monomers randomly connect with olefinic unsaturated acid monomers on the same polymer chain to form a polymer chain. Since olefinic unsaturated acid monomers are soft monomers, the resulting acrylic emulsion shell structure is a "soft shell," providing flexibility and cohesiveness, preventing the coating from cracking due to excessive brittleness during drying or storage, and ensuring smooth scraping. It appears as flakes rather than flying powder; during the preparation of the core layer structure of acrylic emulsion, acrylate monomers and styrene polymerize under the action of highly active hydroxyl radicals. Since styrene is a hard monomer, the final core is a "hard core", which can give the coating film enough brittleness so that it can be cut by a blade and peel off in flakes when scratched, rather than being stretched into filaments or torn incompletely. This "soft on the outside and hard on the inside" core-shell design allows the coating film to have enough strength to maintain complete coverage at room temperature, and to break neatly along the stress point when subjected to shear force, achieving a user experience that is easy to scrape, dust-free, and with clear edges.

[0020] In this invention, the acrylate monomers are preferably alkyl acrylates and / or alkyl methacrylates; the alkyl acrylates preferably include one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, isooctyl acrylate, n-propyl acrylate, and cyclohexyl acrylate, more preferably n-butyl acrylate; the alkyl methacrylates preferably include one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-propyl methacrylate, cyclohexyl methacrylate, tridecyl methacrylate, and octadecyl methacrylate, more preferably methyl methacrylate. As one embodiment, the acrylate monomers can be a mixture of n-butyl acrylate and methyl methacrylate; the mass ratio of n-butyl acrylate to methyl methacrylate in the mixture can be (35~50):(50~60), or it can be (40~45):(55~58).

[0021] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 0.1 to 10 parts of olefinic unsaturated acid monomers, based on 100 parts by mass of acrylate monomers; the olefinic unsaturated acid monomers are preferably acrylic acid and / or methacrylic acid. As one embodiment, the mass parts of the olefinic unsaturated acid monomers can be 0.2 parts, 0.5 parts, 1 part, 2 parts, 2.3 parts, 3 parts, 5 parts, 6 parts, or 8 parts. In the present invention, the olefinic unsaturated acid monomers are functional monomers. Because olefinic unsaturated acid monomers are hydrophilic, they tend to distribute on the surface of micelles / latex particles rather than being deeply embedded inside. After copolymerization with acrylate monomers, they form latex particles with polyacrylate as the main chain and a large number of carboxyl groups on the side chains, ultimately forming the shell layer of the core-shell structured acrylic emulsion. Furthermore, the olefinic unsaturated acid monomers are soft monomers, which can improve the toughness of the shell layer.

[0022] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 1 to 20 parts of styrene, based on 100 parts by mass of acrylate monomers. As one embodiment, the mass of styrene can be 2 parts, 5 parts, 5.7 parts, 8 parts, 10 parts, 12 parts, 15 parts, or 18 parts. In the present invention, when styrene copolymerizes in the core layer, it can significantly reduce the hydrophilicity of the core layer. The hydrophobic core layer can effectively block water molecule penetration, greatly improving the ink layer's wet rubbing resistance and anti-whitening properties. Furthermore, styrene is a hard monomer, which can increase the hardness of the core, forming a "soft outside, hard inside" core-shell design with the soft shell.

[0023] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 0.05 to 2 parts of emulsifier, based on 100 parts by mass of acrylate monomers; the emulsifier is preferably the anionic emulsifier Disponil FES32. As one embodiment, the mass parts of the emulsifier can be 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, 1, 1.2, 1.4, 1.5, 1.6, or 1.8 parts. In this invention, after the emulsifier is mixed with water, the emulsifier molecules self-assemble to form micelles (hydrophobic groups facing inward and hydrophilic groups facing outward). This allows the hydrophobic acrylate and the hydrophilic olefinic unsaturated acid monomers to copolymerize within the micelles. Since the olefinic unsaturated acid monomers are hydrophilic, they tend to be distributed on the outer layer of the micelles / particles (close to the aqueous phase) after polymerization, thus achieving a structure design where the "shell" is rich in carboxyl groups. When a neutralizing agent is added at the end to adjust the pH, the latex particles converted from the emulsifier micelles already have a negative charge provided by the emulsifier. Combined with the negative charge from the ionization of carboxyl groups, a dual stabilization mechanism is formed, which has a good dispersion and anchoring effect on pigments such as carbon black. Even with a high content of pigment, it can still maintain low viscosity, good fluidity, and non-settling properties. After the black ink dries into a film, the hydrophobic cores are tightly packed to form a dense film structure, which blocks the pigment and ensures uniform hiding power, no pinholes, and no light-transmitting points.

[0024] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 0.01 to 1 part initiator, based on 100 parts by mass of acrylate monomers; the initiator is preferably one or more selected from potassium persulfate, ammonium persulfate, and sodium persulfate. As one embodiment, the initiator may be 0.02 parts, 0.03 parts, 0.05 parts, 0.08 parts, 0.1 parts, 0.14 parts, 0.2 parts, 0.5 parts, 0.6 parts, or 0.8 parts by mass. In the present invention, the initiator decomposes under heating conditions to generate primary free radicals, which enter the micelles or aqueous phase, preparing for polymerization initiation.

[0025] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention, based on 100 parts by mass of acrylate monomers, preferably include 0.1 to 3 parts of a neutralizing agent; the neutralizing agent is preferably ammonia water, more preferably ammonia water with a mass concentration of 25%. As one embodiment, the mass parts of the neutralizing agent can be 0.2 parts, 0.5 parts, 0.8 parts, 1 part, 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, or 2.5 parts. In the present invention, after the polymerization reaction is completed, the system contains a large number of latex particles with carboxyl groups (-COOH). At this time, the carboxyl groups are hydrophobic or weakly hydrophilic, the viscosity of the emulsion is low, and the stability is limited. After adding the neutralizing agent, the carboxyl groups are neutralized into carboxylate anions (-COOH). -When the latex particles are negatively charged, strong electrostatic repulsion is generated between them, preventing aggregation and thus achieving chemical stability. At the same time, when the neutralizing agent is ammonia, the carboxylate ions will undergo hydration and combine with water molecules. At this time, the carboxylate ions in the shell endow the latex particles with hydrophilicity. This hydrophilic shell can protect the internal hydrophobic core and improve the adhesion to the substrate.

[0026] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention, based on 100 parts by mass of acrylate monomers, preferably include 0.001 to 0.005 parts by mass of catalyst; the catalyst is preferably ferrous sulfate heptahydrate and disodium ethylenediaminetetraacetate dihydrate; the mass ratio of ferrous sulfate heptahydrate to disodium ethylenediaminetetraacetate dihydrate is preferably (1~2):(1~2), more preferably 1:1. As one embodiment, the mass part of catalyst can be 0.002 parts, 0.003 parts, or 0.004 parts. In the present invention, the catalyst, oxidant, and reductant can form a composite system. Ferrous ions in the catalyst are converted into ferric ions under the action of the oxidant, while highly active hydroxyl radicals are generated. The ferric ions are then reduced back to ferrous ions under the action of the reductant, allowing the catalyst to be recycled.

[0027] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention, based on 100 parts by mass of acrylate monomers, preferably include 0.1 to 0.5 parts by mass of an oxidant; the oxidant is preferably a tert-butyl hydrogen peroxide solution, more preferably a 70% tert-butyl hydrogen peroxide solution. As one embodiment, the oxidant may be 0.13, 0.2, 0.3, or 0.4 parts by mass. In the present invention, the main function of the oxidant is to convert ferrous ions in the catalyst into ferric ions, while simultaneously generating highly reactive hydroxyl radicals.

[0028] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention preferably include 0.1 to 1 part of a reducing agent, based on 100 parts by mass of acrylate monomers; the reducing agent is preferably Bruggolite® FF6M manufactured by Bruggolite AG, Germany. As one embodiment, the mass fraction of the reducing agent can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, or 0.9 parts. In the present invention, the reducing agent can reduce ferric ions back to ferrous ions, allowing the catalyst to be recycled.

[0029] The raw materials for preparing the core-shell structured acrylic emulsion of the present invention, based on 100 parts by mass of acrylate monomers, preferably include 60-150 parts of water; the water is preferably deionized water. As one embodiment, the mass fraction of water can be 70, 80, 90, 100, 110, 120, 130, or 140 parts. In the present invention, water serves as a solvent, primarily providing the reaction environment for the reaction system.

[0030] In this invention, the method for preparing the core-shell structured acrylic emulsion preferably includes the following steps: 1) Mix some acrylate monomers, olefinic unsaturated acid monomers, emulsifiers, initiators and some water to carry out the first polymerization reaction, and then add a neutralizing agent to obtain a shell emulsion; 2) Divide the remaining water into two parts. Mix one part with the oxidant to form an oxidant solution, and mix the other part with the reducing agent to form a reducing agent solution. Add the remaining acrylate monomers and styrene to the shell emulsion obtained in step 1) and stir until homogeneous. Then add the catalyst, oxidant solution and reducing agent solution in sequence to carry out the second polymerization reaction. Then filter to obtain a core-shell structured acrylic emulsion.

[0031] In this invention, a portion of acrylate monomers, olefinic unsaturated acid monomers, emulsifiers, initiators, and a portion of water are mixed to carry out a first polymerization reaction, and then a neutralizing agent is added to obtain a shell emulsion.

[0032] In this invention, the mass of the acrylate monomers is preferably 20-40% of the total mass of the acrylate monomers; the mass of the water is preferably 60-90% of the total mass of the water. As one embodiment, the mass of the acrylate monomers is preferably 25%, 30%, or 35% of the total mass of the acrylate monomers; the mass of the water is preferably 65%, 70%, 75%, 80%, 85%, or 87.5% of the total mass of the water. By controlling the amount of acrylate monomers used, this invention can effectively control the ratio of the shell and core layers in a core-shell structured acrylic emulsion.

[0033] In this invention, the preferred method for mixing the acrylate monomers, olefinic unsaturated acid monomers, emulsifiers, initiators, and a portion of water is as follows: first, the emulsifier and a portion of water are mixed and heated to 80-90°C, then the initiator is added, followed by the dropwise addition of a mixture of acrylate monomers and olefinic unsaturated acid monomers.

[0034] In this invention, the preferred temperature for the first polymerization reaction is 80-90°C, more preferably 85°C. This invention does not impose a specific limitation on the dropping rate; based on the technical knowledge of those skilled in the art, it is sufficient to ensure that the mixture of acrylate monomers and olefinically unsaturated acid monomers is fully mixed and reacted. This invention does not impose a specific limitation on the time of the first polymerization reaction; based on the technical knowledge of those skilled in the art, it is sufficient to ensure that the polymerization reaction is complete. In this invention, after the emulsifier is mixed with water, the emulsifier molecules self-assemble to form micelles (hydrophobic groups facing inward and hydrophilic groups facing outward). Acrylic monomers diffuse into the activated micelles through the aqueous phase and initiate chain growth reactions through free radicals. The acrylate monomers and olefinic unsaturated acid monomers are randomly linked on the same polymer chain to form a polymer chain, thereby enabling the copolymerization of hydrophobic acrylate monomers and hydrophilic olefinic unsaturated acid monomers. Since the olefinic unsaturated acid monomers are hydrophilic, they tend to be distributed on the outer layer of the micelles / particles (close to the aqueous phase) after polymerization, thus achieving a structure design with a "shell" rich in carboxyl groups. When a neutralizing agent is added at the end to adjust the pH, the latex particles converted from the emulsifier micelles already have a negative charge provided by the emulsifier, plus the negative charge from the ionization of carboxyl groups, forming a dual stabilization mechanism.

[0035] In this invention, the neutralizing agent is preferably added dropwise. The present invention does not impose any particular limitation on the dropwise addition rate, which can be determined based on the technical knowledge of those skilled in the art.

[0036] After obtaining the shell emulsion, the present invention preferably further includes cooling the shell emulsion; the endpoint temperature of the cooling is preferably ≤50°C. Cooling facilitates the subsequent second polymerization reaction.

[0037] In this invention, the pH value of the shell emulsion is preferably 7.5 to 8.0. By controlling the pH value of the shell emulsion, this invention can achieve good stability.

[0038] After obtaining the shell emulsion, the present invention divides the remaining water into two parts. One part is mixed with an oxidant to form an oxidant solution, and the other part is mixed with a reducing agent to form a reducing agent solution. The remaining acrylate monomers and styrene are added to the shell emulsion and stirred evenly. Then, a catalyst, an oxidant solution and a reducing agent solution are added in sequence to carry out a second polymerization reaction. After filtration, a core-shell structured acrylic emulsion is obtained.

[0039] This invention does not impose specific limitations on the concentrations of the oxidant and reducing agent solutions; the concentrations are determined based on the technical knowledge of those skilled in the art, as long as they are completely dispersed. This invention utilizes the system between the catalyst, oxidant, and reducing agent to generate a large number of highly reactive hydroxyl radicals, promoting the polymerization of acrylate monomers with styrene to form a highly hydrophobic core layer.

[0040] In this invention, the interval between the addition of the catalyst, oxidant solution, and reducing agent solution is preferably 10-30 minutes, more preferably 20 minutes. By controlling the interval between the addition of the catalyst, oxidant solution, and reducing agent solution, this invention facilitates the full progress of the polymerization reaction.

[0041] In this invention, the product of the second polymerization reaction is preferably cooled to ≤40°C before filtration; the filtration method is preferably using a 200-mesh filter cloth. This invention removes unreacted impurities through filtration.

[0042] In this invention, the core-shell structured acrylic emulsion consists of a hard core composed of hard monomers such as styrene and methyl methacrylate, which gives the coating sufficient brittleness so that it can be cut off by a blade and peel off in sheets when scraped, rather than being stretched into filaments or torn incompletely. The soft shell is composed of soft monomers such as butyl acrylate and hydrophilic monomers, which can provide flexibility and cohesion, preventing the coating from cracking due to excessive brittleness during drying or storage. At the same time, it ensures that the coating is scraped off in sheets rather than in powder form. This "soft on the outside and hard on the inside" core-shell design allows the coating to maintain complete coverage at room temperature with sufficient strength, and to break neatly along the stress point when subjected to shear force, achieving a user experience that is easy to scrape off, dust-free, and with clear edges.

[0043] Based on a mass fraction of 30-45 parts of the core-shell structured acrylic emulsion, the water-based scratch-off masking black ink provided by this invention comprises 15-25 parts of an aliphatic waterborne polyurethane dispersion; the aliphatic waterborne polyurethane dispersion is preferably ACURE502 aliphatic waterborne polyurethane dispersion; the preferred parameters of the aliphatic waterborne polyurethane dispersion are: solid content: 34-36%, viscosity at 25°C: <500 mPa·s, pH value: 7.5-9.0, density: 1.06±0.2 g / cm³. 3In one embodiment, the mass fraction of the aliphatic waterborne polyurethane dispersion can be 16, 17, 18, 19, 20, 21, 22, 23, or 24 parts. In this invention, the paint film formed by the aliphatic waterborne polyurethane dispersion has high tensile strength and hardness. This characteristic allows the ink layer formed by the waterborne scrapeable opaque black ink to be relatively "brittle," satisfying the physical basis for scrapeability. The aliphatic waterborne polyurethane dispersion has excellent adhesion to the substrate, resisting friction during daily transportation and use without being so firmly attached that it cannot be scraped off. Simultaneously, the aliphatic waterborne polyurethane dispersion, as a binder, effectively wets and disperses pigments such as carbon black, resulting in a strong opacity and rich color in the ink layer, ensuring that the information before scraping is completely masked. The aliphatic waterborne polyurethane dispersion has suitable viscosity and leveling properties, enabling the formation of a smooth, pore-free ink layer, ensuring neat edges in the scraped area without burrs or residue.

[0044] Based on a core-shell structured acrylic emulsion mass fraction of 30-45 parts, the water-based scratch-off opaque black ink provided by this invention comprises 12-20 parts of carbon black; the carbon black is preferably high-pigment carbon black, more preferably high-pigment carbon black with a particle size of 10-20 nm. As one embodiment, the mass fraction of the carbon black can be 13, 14, 15, 16, 17, 18, or 19 parts. In this invention, carbon black has extremely strong tinting strength, imparting a deep bluish-black to inks and coatings, making it a key pigment for achieving a "high blackness" visual effect.

[0045] Based on 30-45 parts by weight of the core-shell structured acrylic emulsion, the water-based scratch-off opaque black ink provided by this invention comprises 4-8 parts by weight of modified polyethylene wax powder; the modified polyethylene wax powder is preferably Clariant Ceridust 3715. As one embodiment, the modified polyethylene wax powder can be 5, 6, or 7 parts by weight. In this invention, the modified polyethylene wax powder provides the ink layer with excellent scratch resistance and anti-blocking properties, while giving the surface a smooth but non-greasy feel. It protects the ink layer without causing slippage during scratching due to excessive smoothness. During scratching, the rough scratching force damages the wall material, and the released wax forms a lubricating layer with the synthetic ester, significantly reducing scratching resistance and guiding the ink layer to peel off neatly along the interface.

[0046] Based on a mass fraction of 30-45 parts of the core-shell structured acrylic emulsion, the water-based squeezable opaque black ink provided by this invention includes 2-4 parts of a superdispersant; the superdispersant is preferably Lubrizol SOLSPERSE 44000 or Lubrizol SOLSPERSE 46000. As one embodiment, the mass fraction of the superdispersant can be 2.5 parts, 3 parts, or 3.5 parts. By adding a superdispersant, this invention promotes the full dispersion of carbon black in the water-based squeezable opaque black ink, thereby improving the storage stability of the black ink and the final opaque effect.

[0047] Based on 30-45 parts by weight of the core-shell structured acrylic emulsion, the water-based scratch-off opaque black ink provided by this invention includes 0.5-1.5 parts of a wetting and leveling agent; the wetting and leveling agent is preferably Evonik TEGO Wet 238 (Germany), Lencolo 3157 (Germany), or Wyncoat® SL-5100 (China). As one embodiment, the wetting and leveling agent can be in the following proportions: 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts, 1.2 parts, 1.3 parts, or 1.4 parts by weight. In this invention, the wetting property of the wetting and leveling agent occurs the instant that the water-based scrapeable black ink comes into contact with the substrate. The core is to reduce the surface tension of the black ink so that it can overcome the resistance of the substrate surface and spread evenly. The leveling occurs after the black ink is coated and during the drying process, which makes the surface tension of the paint film uniform and eliminates the traces left during coating. This solves the surface defects such as pinholes, orange peel and poor adhesion caused by high pigment carbon black system and low surface energy substrate.

[0048] Based on 30-45 parts by weight of the core-shell structured acrylic emulsion, the water-based scratch-off masking black ink provided by this invention includes 0.2-0.8 parts by weight of defoamer; the defoamer is preferably an organosilicon defoamer, more preferably Evonik TEGO® Foamex 8420. As one embodiment, the defoamer may be 0.3, 0.4, 0.5, 0.6, or 0.7 parts by weight. In this invention, because the superdispersant, wetting and leveling agent, and carbon black introduce a large amount of gas during preparation, use, and printing, relatively stable bubbles are formed in the water-based scratch-off masking black ink, leading to defects such as pores in the ink layer. Therefore, a defoamer is needed to eliminate and suppress the generated bubbles.

[0049] Based on 30-45 parts by weight of the core-shell structured acrylic emulsion, the water-based scratch-off masking black ink provided by this invention includes 0.1-0.5 parts by weight of a pH adjuster; the pH adjuster is preferably 2-amino-2-methyl-1-propanol (AMP-95), dimethylethanolamine (DMEA), or triethanolamine (TEA). As one embodiment, the pH adjuster can be 0.2, 0.3, or 0.4 parts by weight. By adding a pH adjuster, this invention can regulate the pH value of the system, thereby improving the stability of the system.

[0050] Based on a core-shell structured acrylic emulsion mass fraction of 30-45 parts, the water-based scratch-off opaque black ink provided by this invention comprises 15-25 parts water; the water is preferably deionized water. As one embodiment, the mass fraction of the water can be 16, 17, 18, 19, 20, 21, 22, 23, or 24 parts. In this invention, water is used as a solvent.

[0051] Based on 30-45 parts by weight of the core-shell structured acrylic emulsion, the water-based scratch-off opaque black ink provided by this invention includes 1-3 parts of an additive; the additive is preferably a mixture of polyethylene glycol, tributoxyethyl phosphate, and nano-silica; the molecular weight of the polyethylene glycol is preferably 400-600; the particle size of the nano-silica is preferably 20-60 nm; the mass ratio of the polyethylene glycol, tributoxyethyl phosphate, and nano-silica is preferably 5:(2-3):(2-3). As one embodiment, the mass parts of the additive can be 1.2 parts, 1.5 parts, 1.8 parts, 2 parts, 2.2 parts, 2.5 parts, or 2.8 parts. In this invention, polyethylene glycol can act as an internal plasticizer to solve the problem of ink layer brittleness, preventing it from pulverizing (breaking into powder) when scraped, thus giving the ink layer an ideal "brittle but not shattered" state. It can also improve the leveling and wetting properties of black ink, and enhance the dispersion performance of nanoparticles such as carbon black. Tributoxyethyl phosphate can improve the antifreeze and flame retardancy of black ink, and further eliminate air bubbles. Adding an appropriate amount of nano-silica can increase hardness, which helps to increase the brittleness of the ink layer, making it easier to scrape.

[0052] The present invention also provides a method for preparing the water-based scratch-off opaque black ink described in the above technical solution, comprising the following steps: (1) Mix water, superdispersant, part of defoamer and carbon black to obtain carbon black slurry; (2) Mix the carbon black paste, core-shell structured acrylic emulsion and aliphatic waterborne polyurethane dispersion obtained in step (1), then add wetting and leveling agent, additives, remaining defoamer, modified polyethylene wax powder and pH adjuster, and finally filter to obtain waterborne scrapable cover black ink.

[0053] This invention mixes water, a superdispersant, a portion of a defoamer, and carbon black to obtain a carbon black paste.

[0054] In this invention, the mass of the defoamer is preferably 30-70% of the total mass of the defoamer, more preferably 40-60%, and even more preferably 50%. By adding the defoamer in batches, this invention ensures thorough defoaming.

[0055] In this invention, the mixing of water, superdispersant, partial defoamer, and carbon black is preferably carried out sequentially with dispersion and grinding; the dispersion speed is preferably 1000-1500 r / min; the dispersion time is preferably 30-45 min; and the grinding is preferably performed until the fineness of the carbon black slurry is ≤10 μm. In this invention, the dispersion is preferably carried out in a dispersion kettle; and the grinding is preferably carried out in a sand mill. As one embodiment, the dispersion speed can be 1050 r / min, 1100 r / min, 1150 r / min, 1200 r / min, 1250 r / min, 1300 r / min, 1350 r / min, 1400 r / min, or 1450 r / min; and the dispersion time can be 35-40 min. This invention does not have a specific limitation on the specific source of the dispersion kettle and sand mill; commercially available dispersion kettles and sand mills well known to those skilled in the art can be used. By using the above-described mixing method, this invention can uniformly disperse carbon black in the color slurry, forming a uniform black carbon slurry.

[0056] After obtaining the carbon black paste, the present invention mixes the carbon black paste, core-shell structured acrylic emulsion and aliphatic waterborne polyurethane dispersion, then adds wetting and leveling agent, additives, remaining defoamer, modified polyethylene wax powder and pH adjuster, and finally filters to obtain waterborne scrapable cover black ink.

[0057] In this invention, the preferred method for mixing the carbon black slurry, the core-shell acrylic emulsion, and the aliphatic aqueous polyurethane dispersion is as follows: the core-shell acrylic emulsion and the aliphatic aqueous polyurethane dispersion are mixed, and then the carbon black slurry is added under stirring conditions. The stirring rate is preferably 400-600 r / min, more preferably 450-550 r / min, and even more preferably 500 r / min. This invention does not impose a specific limitation on the addition rate of the carbon black slurry; it can be determined based on the technical knowledge of those skilled in the art, as long as it ensures uniform mixing. By employing the above-described mixing method, this invention enables uniform mixing of all components.

[0058] In this invention, the preferred method for adding the wetting and leveling agent, additives, remaining defoamer, modified polyethylene wax powder, and pH adjuster is as follows: First, add the wetting and leveling agent, additives, and remaining defoamer at a stirring rate of 400-600 r / min, and stir for 10-20 min after all additions. Then, add the modified polyethylene wax powder at a stirring rate of 100-300 r / min, and stir for 10-15 min after all additions. Subsequently, add the pH adjuster at a stirring rate of 100-300 r / min to adjust the pH value to 8.0-8.8, and stir for 5-15 min after all additions. By adding the components in the above manner, this invention ensures thorough mixing of the components while preventing the agglomeration of nanoparticles such as carbon black.

[0059] In this invention, the filtration is preferably performed using a 200-mesh filter. This invention removes agglomerated particles through filtration.

[0060] The preparation method provided by this invention is simple and does not require complex and expensive equipment, which is conducive to large-scale industrial application.

[0061] The present invention also provides the application of the water-based scratch-off cover ink described above in flexographic printing for the preparation of instant lottery tickets, prize-winning invoices, or anti-counterfeiting labels.

[0062] The present invention does not impose any special limitations on the specific operation of the application, and any application method known to those skilled in the art can be used.

[0063] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0064] The sources and preparation methods of the raw materials used in the embodiments and comparative examples of this invention are as follows: The raw materials for preparing the core-shell structured acrylic emulsion, by mass parts, are 100 parts of acrylate monomers, 2.3 parts of olefinic unsaturated acid monomers, 1.2 parts of emulsifier, 0.14 parts of initiator, 1 part of neutralizer, 0.003 parts of catalyst, 0.13 parts of oxidant, 0.2 parts of reducing agent, 5.7 parts of styrene, and 120 parts of water; The acrylate monomers are a mixture of methyl methacrylate and n-butyl acrylate, with 46 parts methyl methacrylate and 54 parts n-butyl acrylate; the olefinic unsaturated acid monomers are acrylic acid; the emulsifier is the anionic emulsifier Disponil FES32 (BASF, fatty alcohol polyoxyethylene ether (4EO) ammonium sulfate, 32% active ingredient content); the initiator is ammonium persulfate; the neutralizing agent is 25% ammonia water; the catalyst is a mixture of ferrous sulfate heptahydrate and disodium ethylenediaminetetraacetate dihydrate in a 1:1 mass ratio; the oxidizing agent is a 70% tert-butyl hydrogen peroxide solution; the reducing agent is Bruggolite® FF6M manufactured by Bruggolite AG, Germany; and the water is deionized water. The preparation method of the core-shell structured acrylic emulsion includes the following steps: 1) First, mix the emulsifier and 90 parts by mass of water and heat to 85°C. Then add the initiator, followed by the dropwise addition of a mixture of 30 parts of acrylate monomers (20 parts of methyl methacrylate and 10 parts of n-butyl acrylate) and olefinic unsaturated acid monomers. The first polymerization reaction is carried out at 85°C. Finally, add the neutralizer and cool to 50°C to obtain a shell emulsion with a pH of 7.5. 2) Mix the oxidant with 18 parts by mass of water to form an oxidant solution, and mix the reducing agent with 12 parts by mass of water to form a reducing agent solution. Add 70 parts of acrylate monomers (26 parts of methyl methacrylate and 44 parts of n-butyl acrylate) and styrene to the shell emulsion obtained in step 1) and stir evenly. Then, add the catalyst (and keep warm for 20 min after addition), the oxidant solution (and keep warm for 20 min after addition), and the reducing agent solution (and keep warm for 20 min after addition) in sequence to carry out the second polymerization reaction. Finally, cool down to 40°C and filter using a 200-mesh filter cloth to obtain a core-shell structured acrylic emulsion.

[0065] The aliphatic waterborne polyurethane dispersion is ACURE502 aliphatic waterborne polyurethane dispersion; the parameters of the aliphatic waterborne polyurethane dispersion are: solid content: 35%, viscosity at 25℃: <500 mPa·s, pH value: 8.0, density: 1.06 g / cm³. 3 ; The carbon black is a high-pigment carbon black with a particle size of 10-20 nm. The modified polyethylene wax powder is Clariant Ceridust 3715; The superdispersant is Lubrizol SOLSPERSE 44000; The wetting and leveling agent is Evonik TEGO Wet 238 from Germany; The defoamer is Evonik TEGO® Foamex 8420; The pH adjuster is triethanolamine; The water is deionized water; The additive is a mixture of polyethylene glycol, tributoxyethyl phosphate and nano silica; the molecular weight of the polyethylene glycol is 400-600; the particle size of the nano silica is 20-60 nm; and the mass ratio of the polyethylene glycol, tributoxyethyl phosphate and nano silica is 5:3:2.

[0066] Example 1 A water-based, scratch-off, opaque black ink, by weight, is composed of the following components: 30 parts core-shell structured acrylic emulsion, 20 parts aliphatic waterborne polyurethane dispersion, 15 parts carbon black, 6 parts modified polyethylene wax powder, 3 parts superdispersant, 1 part wetting and leveling agent, 0.6 parts defoamer, 0.4 parts pH adjuster, 20 parts water, and 2 parts additives. The preparation method of the water-based scratch-off cover ink is as follows: (1) Water, superdispersant, partial defoamer and carbon black are mixed and dispersed in a dispersion vessel, and then ground in a sand mill to a fineness of ≤10μm to obtain carbon black slurry; the mass of the partial defoamer is 40% of the total mass of the defoamer; the dispersion speed is 1500r / min and the dispersion time is 40min; (2) Mix the core-shell structured acrylic emulsion and the aliphatic waterborne polyurethane dispersion, and then add the carbon black paste obtained in step (1) at a stirring rate of 500 r / min. Next, add the wetting and leveling agent, the additive and the remaining defoamer at a stirring rate of 500 r / min. After all the additives are added, stir for 20 min. Then, add the modified polyethylene wax powder at a stirring rate of 300 r / min. After all the additives are added, stir for 15 min. Then, add the pH adjuster at a stirring rate of 200 r / min to adjust the pH value. After all the additives are added, stir for 10 min. Finally, filter with a 200-mesh filter to obtain waterborne scrapable cover black ink.

[0067] Example 2 A water-based scratch-off cover ink is provided, wherein the mass fraction of the core-shell structured acrylic emulsion is modified to 35 parts, and other conditions are the same as in Example 1.

[0068] Example 3 A water-based scratch-off cover ink is provided, wherein the mass fraction of the core-shell structured acrylic emulsion is modified to 40 parts, and other conditions are the same as in Example 1.

[0069] Comparative Example 1 A water-based scratch-off cover ink is provided, wherein the mass fraction of the core-shell structured acrylic emulsion is modified to 0 parts, and other conditions are the same as in Example 1.

[0070] Comparative Example 2 A water-based scratch-off cover ink is provided, wherein the mass fraction of the core-shell structured acrylic emulsion is modified to 5 parts, and other conditions are the same as in Example 1.

[0071] Comparative Example 3 A water-based scratch-off cover ink is provided, wherein the mass fraction of the core-shell structured acrylic emulsion is modified to 60 parts, and other conditions are the same as in Example 1.

[0072] The basic properties of the water-based scratch-off opaque black inks of Examples 1-3 and Comparative Examples 1-3 were tested. Appearance was directly observed. Fineness was tested using the GB / T 13217.3-2008 method, and pH value was measured using a pH meter. The results are shown in Table 1. Table 1. Basic properties of water-based scratch-off opaque black inks from Examples 1-3 and Comparative Examples 1-3

[0073] As shown in Table 1, changes in the content of core-shell acrylic emulsion have little impact on the appearance and fineness of water-based scrape-off opaque black ink. This is because the color of the appearance is mainly affected by pigments such as carbon black and dispersibility, while the fineness is mainly affected by the preparation process when the raw materials are the same or similar. The pH value is mainly affected by the dosage of pH adjuster. In Comparative Examples 1 and 2, the dosage of core-shell acrylic emulsion was significantly reduced, while the dosage of other components remained unchanged, resulting in an increase in the relative dosage of pH adjuster during the preparation process, which led to a corresponding increase in the pH value. In Comparative Example 3, the pH value decreased because the excessive dosage of core-shell acrylic emulsion led to a decrease in the relative dosage of pH adjuster.

[0074] The printability of the water-based scratch-off opaque black inks of Examples 1-3 and Comparative Examples 1-3 was tested. The test method was as follows: the printability of the water-based scratch-off opaque black inks was tested on an instant ticket printing machine. At a printing speed of 300 m / min, continuous printing for more than 12 hours showed that the black inks had good transfer and leveling properties, no serious bubbling, good resolubility, and no issues such as dirty printing plates or sticking to rollers. The black inks had good printability and solved the printing slippage and smearing problems that are easily caused by conventional wax powders.

[0075] The volatile organic compounds (VOCs) content in the water-based scratch-off opaque black inks of Examples 1-3 was tested according to the national standard GB 38507-2020. The results showed that the volatile organic compound (VOCs) content in the water-based scratch-off opaque black inks of Examples 1-3 all met the limit requirements for water-based inks and complied with environmental protection requirements.

[0076] The content of harmful metal elements in the water-based scratch-off masking black ink of Examples 1-3 was tested according to the national standard GB / T 26394-2011. The results were as follows: the content of Sb in the water-based scratch-off masking black ink of Examples 1-3 was ≤10mg / kg, the content of As was ≤5mg / kg, the content of Cd was ≤5mg / kg, the content of Pb was ≤10mg / kg, and Hg was not detected.

[0077] According to the national standard GB / T 26394-2011, the peel strength of the water-based squeezable opaque black ink of Examples 1-3 was tested, and the results were: the peel strength of the water-based squeezable opaque black ink of Examples 1-3 was ≥0.8N / 15mm.

[0078] The scratch-off performance of the water-based scratch-off black inks in Examples 1-3 and Comparative Examples 1-3 was tested according to the national standard GB / T 6739-2022 "Determination of Hardness of Paints and Varnishes by Pencil Method". The results are shown in Table 2. Table 2. Scratching performance of water-based scrape-off covering black ink in Examples 1-3 and Comparative Examples 1-3

[0079] As shown in Table 2, the water-based squeegeeable opaque black inks of Examples 1-3 all exhibited excellent squeegee performance at room temperature, while the squeegee values ​​of Comparative Examples 1 and 2 showed a significant decrease. This indicates that omitting or using too little core-shell structured acrylic emulsion affects the squeegee performance of the water-based squeegeeable opaque black ink. After being placed at 80±5℃ for 24 hours, the squeegee values ​​all increased to varying degrees. Among them, the increase in the squeegee value of Comparative Example 3 was greater than that of Examples 1-2, indicating that adding too much core-shell structured acrylic emulsion is not conducive to improving the heat resistance stability of the ink layer. After being placed at -20℃ for 48 hours, the tests showed that Examples 1-3 did not show significant changes compared to room temperature, while the squeegee values ​​of Comparative Examples 1-2 increased significantly, indicating that core-shell structured acrylic emulsion can improve the squeegee performance of the ink layer at low temperatures.

[0080] According to the national standard GB / T 250-2008, the ink layer impermeability and hardness of the water-based scratch-off opacifying black inks of Examples 1-3 and Comparative Examples 1-3 were tested. The impermeability test method was as follows: a standard black and white opacity test card (Leneta card) was prepared, and water-based scratch-off opacifying black ink was coated on the pure white and pure black base plates of the test card respectively using an automatic coater to form a wet film with a thickness of 20 μm. After the wet film was completely dry, the reflectance of the water-based scratch-off opacifying black ink in the white area and the reflectance in the black area were measured using a reflectance meter, and then the contrast ratio (CR) was calculated. Contrast ratio (CR) = black base reflectance / white base reflectance. The hardness test standard was GB / T6739-2006 (Determination of paint film hardness by pencil method for colored paints and varnishes). The results are shown in Table 3. Table 3 shows the ink layer impermeability and hardness of water-based scrape-off black ink in Examples 1-3 and Comparative Examples 1-3.

[0081] As shown in Table 3, when the amount of core-shell acrylic emulsion added is too small or not added at all, the ink layer's opacity decreases slightly. This is because the core-shell structure of the acrylic emulsion can improve the density of the ink layer, thereby increasing its hiding power and concealing information beneath the ink layer. However, if too much core-shell acrylic emulsion is added, the relative content of carbon black will decrease, leading to a reduction in its hiding power. Meanwhile, in Comparative Examples 1 and 2, when no emulsion was added or only a small amount was added, the hardness of the ink layer significantly increased. However, correspondingly, the resistance to breakage decreased, resulting in a high risk of breakage. Conversely, if too much emulsion is used, the hardness will be low, increasing the difficulty of scraping. This demonstrates that the present invention, by controlling the amount of core-shell acrylic emulsion, can regulate the balance between ink layer toughness, resistance to breakage, and scraping properties.

[0082] The ink layers (20 μm) formed by the water-based squeegeeable opaque black ink prepared in Examples 1-3 were kept at -5℃ and 5℃ for 2 hours respectively, and then subjected to bending tests. The results showed that the ink layers had no cracks and peeled off in continuous flakes when squeegeed, without generating dust. In contrast, the ink layers formed by the water-based squeegeeable opaque black ink prepared in Comparative Examples 1-2 cracked when subjected to the same test, and the amount of dust increased when squeegeed. This comparison demonstrates that the present invention, by adding a core-shell structured acrylic emulsion, constructs a microscopic "hard skeleton-soft matrix" morphology within the ink layer. This morphology effectively dissipates energy and prevents crack propagation when subjected to low-temperature bending, thus solving the problem of low-temperature brittleness in traditional water-based inks.

[0083] Example 4 A water-based, scratch-off, opaque black ink, by weight, is composed of the following components: 40 parts core-shell structured acrylic emulsion, 15 parts aliphatic waterborne polyurethane dispersion, 15 parts carbon black, 6 parts modified polyethylene wax powder, 3 parts superdispersant, 1 part wetting and leveling agent, 0.6 parts defoamer, 0.4 parts pH adjuster, 20 parts water, and 2 parts additives. The preparation method of the water-based scratch-off cover ink is the same as in Example 1.

[0084] Example 5 A water-based scratch-off masking black ink, wherein the mass fraction of the aliphatic waterborne polyurethane dispersion is modified to 20 parts, and other conditions are the same as in Example 4.

[0085] Example 6 A water-based scratch-off masking black ink, wherein the mass fraction of the aliphatic waterborne polyurethane dispersion is modified to 25 parts, and other conditions are the same as in Example 4.

[0086] Comparative Example 4 A water-based scratch-off masking black ink, wherein the mass fraction of the aliphatic waterborne polyurethane dispersion is modified to 0 parts, and other conditions are the same as in Example 4.

[0087] The ink layers formed by the water-based squeezable black ink prepared in Examples 4-6 and Comparative Example 4 were squeezed out. The results showed that the edges of the squeezed area of ​​the ink layer formed in Examples 4-6 were neat and without burrs or residues after squeezing out, while a small amount of residue was found at the edges of the squeezed area of ​​the ink layer formed in Comparative Example 4. This indicates that the aliphatic waterborne polyurethane dispersion can further improve the squeezability of black ink.

[0088] Example 7 A water-based, scratch-off, opaque black ink, by weight, is composed of the following components: 40 parts core-shell structured acrylic emulsion, 20 parts aliphatic waterborne polyurethane dispersion, 15 parts carbon black, 6 parts modified polyethylene wax powder, 3 parts superdispersant, 1 part wetting and leveling agent, 0.6 parts defoamer, 0.4 parts pH adjuster, 20 parts water, and 2 parts additives. The preparation method of the water-based scratch-off cover ink is the same as in Example 1.

[0089] Comparative Example 5 A water-based scratch-off cover-up black ink, wherein the mass fraction of modified polyethylene wax powder is changed to 0 parts, and other conditions are the same as in Example 7.

[0090] The water-based scratch-off opaque black inks prepared in Example 7 and Comparative Example 5 were printed on an instant ticket printing machine, with 10 tickets printed for each example. The ink layer thickness was 20 μm, and the ink was dried at room temperature for 2 hours. The 10 tickets were then stacked and manually separated after 24 hours. The results showed that the 10 tickets printed in Example 7 were easily separated without sticking, while the 10 tickets printed in Comparative Example 5 showed obvious sticking during separation. This indicates that the present invention can reduce the adhesion of the water-based scratch-off opaque black ink after drying by adding modified polyethylene wax powder.

[0091] Comparative Example 6 A water-based, scrape-off, cover-up black ink, wherein the mass fraction of the superdispersant is modified to 0 parts, and other conditions are the same as in Example 7.

[0092] Compared with the water-based squeegeeable opaque black ink prepared in Example 7, the water-based squeegeeable opaque black ink prepared in Comparative Example 6 exhibited severe carbon black agglomeration, resulting in poor quality and a poor opacity of the resulting ink layer.

[0093] Comparative Example 7 A water-based scratch-off cover-up black ink, wherein the mass fraction of defoamer is modified to 0 parts, and other conditions are the same as in Example 7.

[0094] Compared with the water-based squeegeeable masking black ink prepared in Example 7, the water-based squeegeeable masking black ink prepared in Comparative Example 7 contains a large number of air bubbles, resulting in a rougher, less smooth ink layer with a poor feel, and it is more susceptible to friction during transportation.

[0095] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water-based, scratch-off, opaque black ink, comprising, by weight parts: 30-45 parts of core-shell structured acrylic emulsion, 15-25 parts of aliphatic waterborne polyurethane dispersion, 12-20 parts of carbon black, 4-8 parts of modified polyethylene wax powder, 2-4 parts of superdispersant, 0.5-1.5 parts of wetting and leveling agent, 0.2-0.8 parts of defoamer, 0.1-0.5 parts of pH adjuster, 15-25 parts of water, and 1-3 parts of additives; The core-shell structured acrylic emulsion comprises a shell polymerized from acrylate monomers and olefinically unsaturated acid monomers, and a core polymerized from acrylate monomers and styrene.

2. The water-based scratch-off cover ink according to claim 1, characterized in that, The core-shell structured acrylic emulsion, by mass fraction, is prepared from raw materials comprising the following components: 100 parts of acrylate monomers, 0.1-10 parts of olefinic unsaturated acid monomers, 1-20 parts of styrene, 0.05-2 parts of emulsifier, 0.05-1 part of initiator, 0.1-3 parts of neutralizer, 0.001-0.005 parts of catalyst, 0.1-0.5 parts of oxidant, 0.1-1 part of reducing agent, and 60-150 parts of water.

3. The water-based scratch-off cover ink according to claim 2, characterized in that, The acrylate monomers are alkyl acrylates and / or alkyl methacrylates; the alkyl acrylates include one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, tert-butyl acrylate, isooctyl acrylate, n-propyl acrylate, and cyclohexyl acrylate; the alkyl methacrylates include one or more of methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, n-propyl methacrylate, cyclohexyl methacrylate, tridecyl methacrylate, and octadecyl methacrylate.

4. The water-based scratch-off cover ink according to claim 2, characterized in that, The olefinic unsaturated acid monomers are acrylic acid and / or methacrylic acid.

5. The water-based scratch-off cover ink according to claim 2, characterized in that, The catalyst is ferrous sulfate heptahydrate and ethylenediaminetetraacetic acid disodium dihydrate; the mass ratio of ferrous sulfate heptahydrate to ethylenediaminetetraacetic acid disodium dihydrate is (1~2):(1~2).

6. The water-based scratch-off cover ink according to any one of claims 2 to 5, characterized in that, The preparation method of the core-shell structured acrylic emulsion includes the following steps: 1) Mix some acrylate monomers, olefinic unsaturated acid monomers, emulsifiers, initiators and some water to carry out the first polymerization reaction, and then add a neutralizing agent to obtain a shell emulsion; 2) Add the remaining acrylate monomers, styrene, catalyst, oxidant, reducing agent and remaining water to the shell emulsion obtained in step 1) to carry out a second polymerization reaction, and then filter to obtain a core-shell structured acrylic emulsion.

7. The water-based scratch-off cover ink according to claim 1, characterized in that, The additive is a mixture of polyethylene glycol, tributoxyethyl phosphate and nano silica.

8. The water-based scratch-off cover ink according to claim 7, characterized in that, The mass ratio of polyethylene glycol, tributoxyethyl phosphate and nano silica is 5:(2~3):(2~3).

9. The method for preparing the water-based scratch-off opaque black ink according to any one of claims 1 to 8, characterized in that, Includes the following steps: (1) Mix water, superdispersant, part of defoamer and carbon black to obtain carbon black slurry; (2) Mix the carbon black paste, core-shell structured acrylic emulsion and aliphatic waterborne polyurethane dispersion obtained in step (1), then add wetting and leveling agent, additives, remaining defoamer, modified polyethylene wax powder and pH adjuster, and finally filter to obtain waterborne scrapable cover black ink.

10. The application of the water-based scratch-off opaque black ink according to any one of claims 1 to 8 or the water-based scratch-off opaque black ink prepared by the preparation method according to claim 9 in the flexographic printing preparation of instant lottery tickets, prize-winning invoices or anti-counterfeiting labels.

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